A conventional loud speaker typically comprises a fixed permanent magnet which interacts with an electromagnet (voice coil) mounted to a diaphragm. By controlling the current supplied to the electromagnet, the diaphragm is driven and the resulting vibrations output acoustic waves. In order to reduce the size and packaging requirements, stronger magnets are required in the loud speakers and these may comprise rare-earth elements, for example neodymium magnets and samarium-cobalt magnets. The use of these types of magnets increases the cost of the speaker devices.
It is known from US 2010/0080406 to provide a push-pull type speaker device comprising first and second diaphragms. A pair of electromagnets, corresponding to the first and second diaphragms, is provided for cooperating with a permanent magnet disposed between the diaphragms. A power source power driver is provided for supplying current to the pair of electromagnets. The winding direction of the electromagnets is reversed such that the pair of electromagnets have opposite magnetic flux directions.
U.S. Pat. No. 2,274,513 discloses an electromagnetic speaker having a diaphragm comprising a magnetic plate moveable between opposing groupings of electromagnets.
U.S. Pat. No. 5,901,235 discloses a planar magnetic transducer comprising a diaphragm having electrical conductors. The diaphragm is mounted between arrays of permanent magnets.
At least in certain embodiments, the present invention sets out to overcome shortcomings associated with the prior art arrangements.